Delaware is a breed that looks just like her, but, with barring. Your girl does not show any indication that she has barring(it is visible only on the black parts of tail and neck, if present). So yours may very well be that cross OR she may be a pure Columbian Rock(I think more likely as her white is very clean with no brown/red leaking anywhere, which is what often happens in a white/black crossed with reds).
BTW I completely agree she's a very nice looking hen, very well taken care off too.